Annual Report 2005 - Fields Institute - University of Toronto

Other issues center around various apparent paradoxes
related to black hole entropy, despite the significant progress
mentioned above, and around the description of the
process of inflation, through which our universe expanded
rapidly from a tiny size to become large and smooth, while
generating the tiny perturbations which eventually grew
into the galaxies and clusters of galaxies that we see today.
The goal of the “Workshop on Gravitational Aspects of
String Theory” was to further explore the implications of
the connections described above, and to chip away at the
fundamental questions which yet remain to be answered.
Organized by Per Kraus, Don Marolf and Amanda Peet as
a part of the thematic program on the Geometry of String
Theory jointly sponsored by the Fields Institute and Perimeter
Institute (in Waterloo), the workshop brought together
approximately 75 theoretical physicists from across North
America and Europe for a week of seminars and discussion.
Discussion and interaction were a central theme of the
workshop: there were no more than four hours of talks
each day, and the talks were presented by a variety of senior
faculty, junior faculty, postdocs, and students. During the
rest of the day the participants were strongly encouraged
to make use of the Fields Institute facilities for numerous
small to medium scale discussions on the above issues.
The result appears to have been a great success, leading one
noted string theorist to state that the meeting was “probably
the best meeting I have been to in a number of years.”
As one would expect from the theme, most of the talks
addressed issues related to black holes and to cosmological
singularities. Gary Horowitz of the University of California
at Santa Barbara discussed an approach in which a
T h e m a t i c P r o g r a m s
Amanda Peet, Don Marolf and Per Kraus
cosmological singularity is mapped to a certain process in
an ordinary quantum field theory via the AdS/CFT correspondence.
As he explained, the hope is that the singularity
might be more tractable in the new language. Bernard de
Wit of Utrecht University and Alex Maloney of Stanford
University described recent progress in using quantum
gravity effects to cloak would-be naked singularities by
event horizons. This leads to black holes whose entropy is
small, but in precise agreement with certain microscopic
computations in string theory, thus extending our microscopic
understanding of black holes. Eva Silverstein of
SLAC described a novel method for removing singularities
by using tachyon condensation to effectively halt the spacetime
evolution before the singularity can form. Another
potential way of avoiding singularities in black holes is to
look for new solutions which look like black holes far away,
but in fact deviate close in such a way that there is no event
horizon or singularity. This approach has been actively
investigated in the past few years, and Simon Ross of the
University of Durham described some recent progress.
Another type of pathology in gravity is the potential existence
of closed timelike curves (“time machines”). Miguel
Costa of Porto University discussed a mechanism for excising
them from the spacetime using stringy effects.
An interesting development in the past year has been the
discovery of new black ring solutions. These are black holes
whose event horizons are not spherical, but instead have a
ring topology. The workshop heard four talks by the pioneers
in this subject: Henriette Elvang and Harvey Reall of
the University of California at Santa Barbara, David Mateos
of the Perimeter Institute, and Roberto Emparan of the
University of Barcelona.
Fields Institute 2005 ANNUAL REPORT 29